Why Antennas Matter
I have mentioned several times that the right antenna solves many problems with network communication reliability. This conclusion is based on experiments I conducted to set up a main node that covers traffic throughout my apartment and also works outdoors, contributing to communication with nearby nodes (up to 3 km in rugged terrain). Since this is a stationary outdoor node with limited access but well-positioned, I estimate that the collinear antenna I built has a gain of around 6–8 dBi (it is 110 cm long!). In Brno, it is used on the ZR10 node, which also runs the “ping” service mentioned later in the text.
During my experiments, I frequently encountered frustration due to a lack of reliable resources that would help me diagnose and resolve issues. Over time, I realized that I needed a quick way to determine the received signal level (RSSI and SNR, which can be read directly from the Meshtastic device) and understand the basic parameters of the antennas used. The specifications listed on webshops are often misleading and insufficient.
To address this, I purchased a nanoVNA, which allows me to determine the most important antenna parameters, such as tuning. I won’t describe the full functionality of the nanoVNA here, but I will share a “trick” that I use, which can help other laypeople like me.
Basic Rule for Antenna Selection
You need a suitable antenna with enough gain to ensure a good signal. A basic signal check is easy:
- On a device that has been running for at least 15 minutes, check the list of devices displaying SNR/RSSI data.
- Ensure the signal from surrounding nodes meets these minimum thresholds:
- RSSI greater than -115 dBm (absolute minimum)
- SNR higher than -7 dB (absolute minimum)
Understanding RSSI and SNR
- SNR (Signal-to-Noise Ratio): Measures how clear your signal is.
- RSSI (Received Signal Strength Indicator): Measures the strength of the signal.
Imagine a noisy intersection. If someone whispers next to you, it will be hard to hear them—this is like low SNR. If they speak louder, you understand them better—higher SNR. The same applies to Meshtastic signals.
Typical values:
- Short distance (next to the device): RSSI ≈ -46 dBm, SNR ≈ +6 dB
- Longer distance (e.g., 2 km to the nearest node): RSSI ≈ -107 dBm, SNR ≈ +2 dB
Effect of Antenna Gain
Higher gain antennas improve RSSI:
- 4 dBi antenna → ~2.5× stronger signal
- 10 dBi antenna → ~10× stronger signal
- 12 dBi antenna → ~16× stronger signal
However, every connector, meter of coaxial cable, and sharp bend reduces signal strength.
- Best practice: Use no connectors or the shortest possible cable.
- Worst practice: Running a coaxial cable through a window and closing it—this will cause severe signal loss.
Key Antenna Parameters
For laypeople, the most important antenna parameters are:
- Gain [dBi] – Higher values indicate better sensitivity and efficiency.
- Directional Characteristic – Higher gain antennas focus signal in a specific direction.
- Impedance (50 Ω) – Ensures efficient energy transfer between the device and antenna.
- SWR (Standing Wave Ratio) – Should be as low as possible (ideally ≤ 3.0).
Additional Considerations
- Polarization
- Connector type
- Cable length (shorter = better)
- Mechanical fastening
- Bandwidth (must include 868 MHz)
Summary
Choosing the right antenna is crucial for reliable Meshtastic communication. By understanding RSSI/SNR, minimizing cable losses, and selecting a well-matched antenna, you can significantly improve network performance. A nanoVNA is a valuable tool for verifying antenna tuning.
Final Note: The same antenna works for both MF and LF modes since they operate on the same frequency.
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